The present invention relates to the field of computer graphics, and in particular to methods and apparatus for animating computer generated characters. The present invention relates to the field of computer graphics. Many computer graphic images are created by mathematically modeling the interaction of light with a three dimensional scene from a given viewpoint. This process, called rendering, generates a two-dimensional image of the scene from the given viewpoint, and is analogous to taking a photograph of a real-world scene. Animated sequences can be created by rendering a sequence of images of a scene as the scene is gradually changed over time. A great deal of effort has been devoted to making realistic looking rendered images and animations.
Computer-generated animation of characters is accomplished by manipulating a three-dimensional model of a character into a series of bodily positions, or poses, over a sequence of frames. A realistic looking character model is often extremely complex, having millions of surface elements and hundreds or thousands of attributes. Due to the complexity involved with animating such complex models, animation tools often rely on armatures and animation variables to define character animation.
An armature is a “stick figure” representing the character's pose, or bodily position. By moving the armature segments, which are the “sticks” of the “stick figure,” the armature can be manipulated into a desired pose. As the armature is posed by the animator, the animation tools modify character model so that the bodily attitude of the character roughly mirrors that of the armature.
Animation variables are another way of defining the character animation of a complex character model. Animation variables are parameters for functions that modify the appearance of a character model. Animation variables and their associated functions are used to abstract complicated modifications to a character model to a relatively simple control. Animation variables and their associated functions may manipulate armature segments, thereby altering the appearance of the character model indirectly, or manipulate the character model directly, bypassing the armature.
For example, a single animation variable can define the degree of opening of a character's mouth. In this example, the value of the animation variable may manipulate several different parts of the armature and/or modify portions of the character model directly to create a modified character model having a mouth opened to the desired degree.
The functions associated with animation variables, referred to as model components, can be used to create a variety of realistic and artistic effects. For example, model components can be used to create layers of bones, muscle, and fat beneath the surface of a character model, so that the surface or skin of a character model deforms realistically as it is posed. Model components can also be used to simulate the movement of non-rigid features such as hair and cloth. In addition to replicating specific physical phenomena, model components can be used to manipulate the character model according to an algorithm or procedure, such as sculpted shapes, metaballs, and physics simulations.
Model components can be extremely complex and therefore time-consuming to execute. To create artistically effective character animation, an animator often creates a rough version of a scene and then repeatedly fine-tunes the character animation to create desired drama and expression of the final scene. The time needed to execute model components as animators pose and repose character models hinders the efficiency of the animator. In the worst case, an animator may be forced to use simplified “stand-in” character models to create the initial animation, and then wait to see the resulting animation with the final character model. In this situation, the animator is essentially working blind and can only guess at the final result. Conversely, the additional computing resources needed to process model components in a reasonable time, if even possible, substantially increases the costs of creating animation.
It is therefore desirable for a system and method of optimizing the performance of model components such that they can be executed in a reasonable time without consuming undue computing resources. It is further desirable to be able to optimize any type of model component, regardless of its function or complexity.